AQA GCSE Chemistry Chemistry Paper 2 (Foundation), June 2022: Question 1

11 marks · Low Demand difficulty · Short Answer

Identify properties of pure water, determine dissolved solids in sea water using mean and scaling calculations, and identify sodium and chloride ions using chemical tests.

Practise this question

Question

Question 01 consists of seven parts about water analysis. Part 1 asks for the boiling point and pH of pure water chosen from a given box of numbers. Part 2 asks what to use to measure the pH of pure water. Part 3 provides a method for determining dissolved solids in sea water by evaporation and asks to select two pieces of equipment from a list: balance, measuring cylinder, ruler, thermometer, and timer. Part 4 presents Table 1 with four repeats of mass of solid that remained from 50 cm³ sea water (1.73, 1.70, 1.75, 1.78 g) and asks to calculate the mean. Part 5 asks to calculate the mass of dissolved solids in 1000 cm³ from a 50 cm³ sample containing 1.50 g. Parts 6 and 7 ask for the flame colour for sodium ions and precipitate colour for chloride ions tested with nitric acid and silver nitrate, choosing each from a box of three colour options.
Question text

01 This question is about water.

A student investigated pure water.

The student measured:

• the boiling point of pure water

• the pH of pure water.

01.1 Complete the sentences.

Choose answers from the box.

[2 marks]

04 7 10 25 100

Pure water has a boiling point of °C.

Pure water has a pH of .

01.2 What could the student use to measure the pH of pure water?

[1 mark]

A different student investigated sea water.

Sea water contains dissolved solids.

This is the method used.

1. Measure a 50 cm3 sample of the sea water.

2. Heat the sample until all the water has evaporated.

3. Measure the mass of solid that remains.

4. Repeat steps 1 to 3 three more times.

*0021.*3 Which two pieces of equipment were needed in this investigation?

[2 marks]

Tick ( ) two boxes.

Balance

Measuring cylinder

Ruler

Thermometer

Timer 4

01.4 Table 1 shows the results.

Table 1

Sea water sample Mass of solid that remained in grams

11.73

21.70

31.75

41.78

Calculate the mean mass of solid that remained.

*03* [2 marks]

Mean mass = g

01.5 A 50 cm3 sample of sea water from a different source contained 1.50 g of

dissolved solids.

Calculate the mass of dissolved solids in 1000 cm3 of this sea water.

[2 marks]

Mass = g

Sodium chloride is a dissolved solid in sea water.

Sodium chloride contains sodium ions and chloride ions.

01.6 Complete the sentence.

Choose the answer from the box.

*04* [1 mark]

crimson lilac yellow

The student tested sea water for sodium ions using a flame test.

The colour of the flame was .

01.7 Complete the sentence.

Choose the answer from the box.

[1 mark]

brown green white

The student tested sea water for chloride ions by adding nitric acid and

silver nitrate solution.

The colour of the precipitate formed was .

Mark scheme

Show the mark scheme Mark scheme for Question 1 detailing accepted answers and mark allocations: 01.1 awards 1 mark for 100 and 1 mark for 7 in that order; 01.2 awards 1 mark for pH probe / meter or universal indicator (paper / solution); 01.3 awards 2 marks for balance and measuring cylinder; 01.4 awards 1 mark for working (1.73 + 1.70 + 1.75 + 1.78)/4 and 1 mark for 1.74 (g); 01.5 awards 1 mark for working (1.5 × 1000)/50 and 1 mark for 30 (g); 01.6 awards 1 mark for yellow; 01.7 awards 1 mark for white. Total question marks: 11.

Question 1

AO /

Question Answers Extra information Mark

Spec. Ref.

01.1 must be in this order AO1

100 1 4.8.1.1

4.10.1.2

71 RPA8

AO /

Spec. Ref.

01.2 pH probe / meter 1 AO1

4.10.1.2

or RPA8

universal indicator allow wide range indicator

(paper / solution) (paper / solution)

AO /

Spec. Ref.

01.3 balance 1 AO1

4.10.1.2

measuring cylinder 1 RPA8

AO /

Spec. Ref.

01.4 (mean =) AO2

1.73 + 1.70 + 1.75 + 1.78 1 4.10.1.2

4 RPA8

= 1.74 (g) 1

AO /

Spec. Ref.

01.5 (mass =) AO2

1.5 × 1000 1 4.10.1.2

50 RPA8

= 30 (g) 1

AO /

Spec. Ref.

01.6 yellow 1 AO1

4.8.3.1

RPA7

AO /

Spec. Ref.

01.7 white 1 AO1

4.8.3.4

RPA7

Total Question 1 11

How to answer it

Water Purity, Dissolved Solids & Ion Identification

📋 What this question tests

This question assesses core practical knowledge from AQA Required Practical 8 (analysis and purification of water) and Required Practical 7 (chemical tests for ions):

  • Fixed physical properties of pure water (boiling point and neutral pH).
  • Suitable laboratory apparatus for measuring pH, volume, and mass.
  • Calculating a simple mean from experimental repeat data.
  • Direct scaling calculations for dissolved solids (converting from 50 cm³ to 1000 cm³).
  • Flame test colour for sodium ions (Na⁺) and halide precipitation test for chloride ions (Cl⁻).

Question 01.1: Physical Constants of Pure Water

Boiling point and pH of pure water (2 Marks)

✅ Mark Scheme Answers

  • Boiling point: 100 °C [1 mark]
  • pH: 7 [1 mark]

Note: Answers must be given in this exact order.

💡 Key Knowledge

A pure substance boils at a single, fixed, sharp temperature (water boils at 100 °C at standard pressure). Impurities widen the boiling range and elevate the boiling point.

Pure water contains equal concentrations of H⁺ and OH⁻ ions, making it neutral with a pH of 7.

Question 01.2: Measuring pH

Apparatus for measuring pH (1 Mark)

✅ Acceptable Answers

  • pH probe or pH meter
  • Universal indicator (paper or solution)
  • Also allowed: "wide range indicator" (paper or solution)

❌ Common Errors

  • Litmus paper: Litmus only shows if a substance is acidic or alkaline; it does not measure the actual pH value.
  • Methyl orange / Phenolphthalein: These are single-change titration indicators and cannot measure numerical pH.

Question 01.3: Apparatus Selection for Dissolved Solids

Selecting experimental equipment from a method (2 Marks)

✅ Selected Boxes

  • ☑ Balance [1 mark]
  • ☑ Measuring cylinder [1 mark]

🧠 Exam Technique

Scan the method steps directly to match the measurements:

  • "Measure a 50 cm³ sample" → requires a liquid volume measure: Measuring cylinder.
  • "Measure the mass of solid" → requires a mass measure: Balance.

Neither a timer, ruler, nor thermometer is mentioned or needed for evaporating to dryness and finding the residual mass.

Question 01.4: Mean Mass Calculation

Calculating the mean from experimental data (2 Marks)

📐 Step-by-Step Calculation

  1. Sum the repeats:
    1.73 + 1.70 + 1.75 + 1.78 = 6.96 g [1 mark]
  2. Divide by the number of samples (4):
    Mean = 6.96 ÷ 4 = 1.74 g [1 mark]

🧠 Examiner Insight

Check for anomalies first! Here, all four values are very close together (ranging from 1.70 to 1.78), so there are no anomalous results to exclude. Always write out your addition step to secure the method mark even if an arithmetic error occurs.

Award 2 marks for the correct final answer of 1.74 g alone.

Question 01.5: Scaling Dissolved Solids to 1000 cm³

Scaling mass for a larger volume (2 Marks)

📐 Step-by-Step Calculation

Method A (Direct Scaling Factor):

  1. Find the scaling multiplier:
    1000 cm³ ÷ 50 cm³ = 20
  2. Multiply mass by the factor:
    1.50 g × 20 = 30 g

Method B (Unitary Method):

  1. Find mass per 1 cm³: 1.50 ÷ 50 = 0.03 g [1 mark]
  2. Multiply by 1000 cm³: 0.03 × 1000 = 30 g [1 mark]

❌ Common Calculation Traps

  • Inverting the ratio: Dividing 50 by 1000 instead of 1000 by 50.
  • Forgetting units: The answer should be given as pure mass in grams (30 g).
Award 2 marks for the correct final answer of 30 g. Award 1 mark for showing (1.5 × 1000) ÷ 50.

Questions 01.6 & 01.7: Ion Identification Tests

Qualitative tests for sodium (Na⁺) and chloride (Cl⁻) ions (2 Marks)

✅ Mark Scheme Answers

  • 01.6 Flame test: yellow [1 mark]
  • 01.7 Halide test: white [1 mark]

💡 Key Knowledge: Chemical Tests

Flame Test Colours:

  • Lithium (Li⁺): Crimson
  • Sodium (Na⁺): Yellow
  • Potassium (K⁺): Lilac
  • Calcium (Ca²⁺): Orange-red
  • Copper (Cu²⁺): Green

Halide Precipitates (Silver Nitrate + Dilute Nitric Acid):

  • Chloride (Cl⁻): White precipitate (AgCl)
  • Bromide (Br⁻): Cream precipitate (AgBr)
  • Iodide (I⁻): Yellow precipitate (AgI)

🧠 Top Tip for Halide Colours

Remember alphabetical order for halides and their shades from lightest to darkest:

Chloride → White
Bromide → Cream
Iodide → Yellow

Nitric acid is added first to remove any carbonate ions that would create a false white precipitate.

Topics

Chemistry · Required Practicals · C8: Chemical Analysis · C10: Using Resources · Required Practicals

Question and mark scheme from the AQA GCSE Chemistry examination, Chemistry Paper 2 (Foundation), June 2022. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.